You can set criteria that your customers must meet in order to earn reviews.

To edit a coupon, click the edit icon on the coupon to display the popup as shown below. This screen allows you to configure the type of coupon offered, expiry, the minimum purchase amount, which products they apply to, and the value of the coupon. The description is automatically generated based on the value but can be personalized to include your own text.
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Note: A personalized description should still contain the coupon value, so reviewers know what the coupon does.